The present invention relates to an operating method for a single-axle roll stabilization system between the chassis and the body of a two-axle, double-track vehicle, whereby energy for supporting a roll torque of the body may be introduced into the chassis via a controllable actuator.
It is known that various external forces and torques act on the mass of a vehicle body which result in, among other things, a “roll motion,” i.e., a rotational motion of the vehicle body about its longitudinal axis. The external forces are generated essentially by the action of centrifugal force during cornering, characterized by the instantaneous transverse acceleration, and by traveling over asymmetrical, uneven areas of a roadway. The resulting roll torque must ultimately be supported at the wheel contact point between the wheel and the roadway. For the necessary transmission of forces between the vehicle body and the wheel, according to the prior art spring/damper units are provided which are usually supplemented by stabilizers for transmission of the pure roll torques. Stabilizers are typically designed as transversely situated torsion bars rotatably supported on the vehicle body between the wheels of an axle. A transverse stabilizer may be used on the front axle and/or the rear axle. For the most part, spring/damper units as well as stabilizers are designed as passive elements, i.e., without supplying external control power.
Also characterized as prior art are devices for “active roll stabilization,” by means of which roll torques are supported by supplying external power. With regard to the design, essentially a distinction is made between active spring/damper systems and active stabilizers. Particular designs may provide active elements on the front axle and rear axle (two-axle active systems), or may provide active elements on one axle and strictly passive elements on the other axle (single-axle active systems). A significant advantage of the single-axle system is the relative cost benefit compared to the more complex two-axle roll stabilization systems.
In principle, roll stabilization systems are used in order to keep the comfort-determining roll angle of the vehicle body as small as possible (or eliminate it entirely) during cornering, and at the same time, by means of a suitable distribution of the overall roll torque to be supported on the front and rear axles, to achieve a suitable yaw or roll steering effect of the vehicle. Use is made of the fact that a relatively stronger support on an axle, due to the associated increase in the transfer of normal force from the inner wheel to the outer wheel on this axle in conjunction with the degressive tire transverse force characteristic, results in a (relative) reduction of the lateral traction forces on the respective other axle. Thus, a stronger relative support on the front axle results in a stronger understeering response, in contrast to a relatively stronger support on the rear axle, which results in a tendency for an oversteering response.
For strictly passive roll stabilization, complete roll compensation is not possible on account of the finite roll rigidity. Thus, for stationary cornering a roll angle >0° in the direction of the outside of the curve always results, the value of which can only be minimized as the sum of the roll rigidity on the front and rear axles increases. As a result, the roll rigidity cannot be arbitrarily increased due to the conflict of objectives for the roll reaction on asymmetrical, uneven roadways. In addition, for strictly passive roll stabilization the ratio of the roll rigidity of the front axle to that of the rear axle is fixed by the design, so that the ratio of the supported roll torques during cornering, and therefore the roll steering tendency of the vehicle as well, is also fixed.
In contrast, two-axle, active roll stabilization systems offer the possibility of complete roll compensation since resettable torques may be applied not as a reaction to a finite stabilizer torsion, but instead, without any external torsion due to the external introduction of energy. When the torques on the front axle and rear axle are independently controlled, these systems also allow a roll steering effect to be set at will over wide ranges and adapted depending on the situation. However, the high complexity of the system and the associated high system costs are disadvantageous.
Single-axle, active roll stabilization systems likewise provide the possibility, at lower system costs, for optional design of the roll angle during cornering, all the way to full compensation. However, the unavoidable coupling of the roll steering effect to the choice of the particular active roll stabilization torque is disadvantageous. In particular for the target objective of reducing the roll angle for front axle-active systems, an increasingly pronounced understeering response is produced with increasing transverse acceleration; i.e., the vehicle progressively loses responsiveness as the transverse acceleration increases. For the same target objective, corresponding rear axle-active systems result in an increasingly pronounced oversteering response with increasing transverse acceleration. Both response effects have a significant (negative) deviation from the essentially constant roll steering effect which is naturally established for a passive vehicle.
An object of the present invention is to provide a remedy for this described problem; i.e., in this case a single-axle roll stabilization system is considered, for which an improvement of the system or its control is to be provided.
This and other object and advantages are achieved by a method in accordance with the present invention, in which an actuator introduces a stabilizing torque which is opposed to the roll torque and which essentially is represented as the product of a rigidity parameter and the roll angle or an alternative roll angle which corresponds to the roll angle with sufficient accuracy and is derived from a measurable variable, the rigidity parameter being freely selectable or adaptable in driving mode.
Thus, it is proposed to control single-axle, active roll stabilization systems in such a way that for any situation, i.e., for increasing or decreasing transverse acceleration, a constant but selectable roll steering effect primarily results. In one exemplary embodiment, the particular choice of the determining torque distribution, and consequently also the entire roll stabilization potential, may be adaptively modified according to the driving situation.